You'd have to have a very different WW2- One where, perhaps, the Soviet Union and Nazi Germany bleed each other white even moreso than OTL while mostly leaving Britain alone. Something along the lines of the "More rational Nazis" AH cliche, (except one of the better written ones of course
) where Germany makes peace with the Westerners after the fall of France and pours all its efforts into an attack on the Soviet Union. At the same time, you need an Isolationist USA that doesn't even give Lend Lease to the Soviets at least, and for some sort of Franco-British Union to happen that allows Britain to have more resources to be a superpower.
So here's the idea. It's a stretch, but it's probably your best bet:
1940: Nazis somehow make peace with Britain, France and Britain form a Union out of fear of a new attack and start preparing for the next war. Germans take Alsace-Lorraine, leave most of France as part of peace deal and withdraw. American investments help the Franco-British Union rebuild and start to focus on keeping their colonies in good relationships.
1941-5?: Alt-Barbarossa, even more Isolationist USA is willing to financially support F-B but not SU. War drags on a long time, destroying both sides' manpower and slowly turning into SU favor before giving way to stalemate somewhere near B-L line. This isn't a WW1 style stalemate, it's both sides being exhausted on a mobile front that neither side seems able to have the resources to break through but keeps trying to. Even with all of this, Germany slowly losing, but due to no L-L, SU less able to capitalize on it as quickly.
Meanwhile, with American support F-B fights and contains Japan. Huge buildup of military.
1946-7: West declares war on Germany again. Ends with British Atomic bomb and West controlling into poland. SU is exhausted as a power, Baltics and Ukraine possibly break free with Western support after long insurgencies against Nazis and Soviets each (Very, VERY unlikely). Still, SU a superpower.
1947 on: Franco-British Union seen as leading West in every way, with control over Central Europe and Pacific as well as their Empires that, though eventually get independence, they retain a lot of influence over. Even with all this, US industrial and economic might is really what keeps them afloat, but this isolationist US has no desire to lead besides making tons of money.
That's all I've got. it's borderline ASB, but it fits the bill more or less.